Radiator damage and steam trails

[Romani]

Another weird question:

In WWII air combat descriptions and battle footage, when an airplane equipped with a inline engine was hit in the cooling circuit, it left a telltale white steam trail, but I see no mention of this in WWI battle accounts.

I think it must be a matter of volume, WWII engines were much larger and had much more fluid, so when a radiator leaked it left a visible plume... in WWI the steam trail must have been too small to be noticeable.

There's one thing I can't figure out... does a punctured fuel tank leave a visible steam trail or the gasoline just vaporizes in the air? I am interested to know if you could tell when an enemy airplane was hit in the fuel tank, aside from burning and smoking of course.

[Machinbird]

Romani, the visibility of any leakage trail is dependent on the amount of fluid being lost. I have seen fuel leakage trails from jets/turboprops on aircraft that I was not flying formation on. If enough fluid is leaking and you are close enough, you will see it as a white stream.
WWI aircraft combats were at lower (warmer) altitudes than WWII, the cooling systems held less coolant in WWI, and the waste heat rejection was less in WWI, so the coolant would less likely be close to the boiling point. The WWI cooling systems were mostly not pressurized-just circulated. Therefore when puncturing a WWI cooling system, coolant would dribble out in a relatively thin trail.
Fuel systems were pressurized in WWI and a visible puff of vapor from a ruptured tank was usually followed by spectacular pyrotechnics.

[Pfalzman]

Romani:

One of the best known incidents you asked about occurred on August 16, 1917 and involved MvR. On his first patrol after returning from his head wound, he stalked and attacked a British Nieuport 17. According to the Baron's combat report he hit the Nieuport's engine and fuel tank -- but there was no resulting aerial fire. I don't know if he could see the fuel leak or not, but he reported feeling nauseous after flying through "a cloud of gas" from the Nieuport. It was his 58th victory.

Regards,